Dr. Lam Author of
|
|
|
|
|
Continue Reading...
Previous | 1 | 2 | 3 | 4 | 5 | 6 | Next
|
Fat Metabolism
Our bodies need energy to function 24 hours a day. The source of this energy,
however, varies greatly. Before breakfast, glucose from the liver, amino
acids from the muscle and fatty acids from fat cells provide energy. During
and shortly after a meal, the energy generation system reverses. The food
taken in serves as the new source of energy. As food is digested, glucose
from carbohydrate breakdown and amino acids from protein breakdown become
the primary source of energy. The liver stops releasing glucose for energy,
and instead stores the excessive glucose from food as glycogen for later
use. The fat cells also store newly absorbed fats for later use. A hormone
called insulin, which is secreted by the pancreas, regulates this process.
Normally, this function operates like clockwork a few times a day, maintaining
a tight control on our metabolism and regulating our energy generation and
fat storage cycles.
Let us now look more closely into the way fats are metabolized. After a
meal, digestive enzymes from the pancreas are secreted directly into the
small intestines. These enzymes consist of those that break down fats (lipase),
starch and sugar (amylase), lactose (lactase), protein (protease). Fats,
in this process are broken down into fatty acids. Next, the cells lining
the small intestine absorb these fatty acids and convert them into triglycerides. Triglycerides are comprised of three fatty acids attached to a glycerol
molecule. They are also known as blood fats, which are the transportable
and stored form of fats.
During this period, the intestinal cells also produce small amounts of cholesterol
and protein. When combined with the triglyceride, they form chylomicron,
which is the fat-soluble "transport vehicles" that can transport the fats
through the blood stream.
Chylomicrons are one of four major classes of fat-protein packages called
lipoproteins. The other lipoproteins are very-low-density lipoproteins
(VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL).
Lipoproteins are differentiated by how much triglyceride they contain. The
more triglyceride within these particles, the less dense they are and the
more they "float". Chylomicron contains the most triglyceride, followed
by VLDL and LDL. HDL contains the lowest amount of triglyceride.
As chylomicron circulates within the bloodstream, another enzyme called
lipoprotein lipase, secreted from the endothelium, breaks down the triglyceride
of the chylomicron further into fatty acid plus glycerol again. Fatty acids
are then absorbed and carried into the fat cells and converted into triglyceride
and stored for later use. What's left of the chylomicron is poor in triglyceride.
These are called chylomicron remnants and are, subsequently, removed from
the bloodstream by the liver.
This process of fats breaking down into fatty
acids and then recombining them to form triglyceride, packaging them into
chylomicrons, and breaking down the chylomicrons is an on-going process
that never ends.
During meals and shortly thereafter, our main source of triglyceride
are chylomicrons, the blood-fat carriers. When we are sleeping, VLDL becomes
our major source of triglyceride-rich lipoprotein. VLDL are very much like
chylomicrons, except that they contain a little less triglyceride. However,
primarily muscles and not fat tissue take up the fatty acid released from
VLDL. This is an important distinction. Fatty acid released by the chylomicron
is taken up mostly by fat cells, while fatty acids released by VLDL goes
into the muscle cells. Furthermore, as the VLDL loses its triglyceride,
the resulting VLDL remnants, instead of being removed in the liver as in
the case of chylomicrons, is partially converted into LDL. The higher the
LDL, the more likely it is that an excess amount of oxidized LDL cholesterol
will be deposited into the endothelium, where fatty streaks and eventual
plaque formation begins.
Scientific evidence has proven that a diet rich in refined
carbohydrate such as white bread and cakes, or starchy foods
such as pasta, potato and rice breaks down into sugar quickly. Excessive
intakes will lead to an elevated blood sugar, especially after a
meal. This type of diet will result in an increase of insulin secretion from the pancreas,
as the body tries to restore the blood sugar down to a normal level. Insulin,
in addition to its glucose lowering duty, will stimulate the liver to make more triglyceride
and VLDL. One of the most important
factors, that determine how much triglyceride your liver makes, are the
daylong levels of insulin (an indication of the amount of carbohydrate you
take) and fatty acids in your blood. The higher the insulin,
the faster the assembly line of triglyceride production occurs in the liver
from fatty acids and glycerol. A high insulin level also causes the fat
cells to release more fatty acid from storage, making more fatty acids available
for the liver to produce triglyceride. Concurrently, chronic high blood
sugar can lead to a state of insulin resistance, which in turn leads to
an abnormal increase in blood insulin level. This high insulin blood level
triggers the liver's production of triglyceride even further. In the Quebec
Cardiovascular Study, it was found that for each 30% increase in insulin
levels; there was a concurrent 70% increase in risk of heart disease over
a five-year period. Carbohydrates increase
sugar, and sugar increases insulin. It is therefore very important to normalize
insulin levels by modulating carbohydrate intake.
In addition to increased triglyceride production, a high insulin level also stimulates the liver to produce a large
quantity of VLDL as well. This is the triglyceride carrier. When
a high VLDL is released into the blood stream, it raises the blood triglyceride
concentration, causing an increasing risk of coronary heart disease. A high
VLDL in turn leads to a high LDL, as LDL is a metabolite of VLDL. In this
respect, we can now understand how a diet high in carbohydrates can lead
to a rise in blood triglyceride and the "bad" LDL cholesterol. A diet high
in saturated fats
(commonly found in red meat) also increase triglyceride levels leading to
an increase in "bad" LDL cholesterol. In other
words, both an intake high in carbohydrates or saturated fats will lead
to increased triglyceride production.
Triglyceride
The role of triglyceride as a marker of cardiovascular disease cannot be
over-emphasized. A diet high in saturated fats, such as red meat,
is not the only diet that raises serum triglyceride level. It is more important
to note that, a diet high in simple carbohydrates and starchy food (such
as sugar, rice, and wheat respectively) can raise serum triglyceride drastically
through insulin. Only 20% of the ingested sugar load can be
burned or stored as glycogen at any one meal. The remainder 80% will be
converted to triglyceride which can contribute to the buildup of acidity,
or stored as fat deposits.
A high triglyceride blood level is a strong and independent risk factor
for heart attacks among middle-aged and elderly men. In fact, studies have shown that blood triglyceride level is a stronger risk
factor than for total cholesterol alone. It is not known as to
why women appear to be more immune to this other than postulations that
the high level of estrogen may be acting as a protective factor. In this
respect, the exact mechanism is still under investigation.
It is naive to think that taking
complex carbohydrates like fruits (high in fructose and glucose) instead
of simple carbohydrates like cakes will reduce the level of sugar and reduced
triglyceride level. This has been proven wrong. Fruits actually contain
fructose which has the similar effect as glucose and sucrose contained in
cakes, although the speed of breakdown of fructose is slower than glucose.
The net result is very similar. Fruit , however, does offer a variety of
other benefits , including fiber and antioxidants. Switching from cakes to high  sugar content fruits such as watermelons will not bring down the
triglyceride level.
In a clinical trial conducted at the University of Minnesota, researchers
reviewed 24 healthy adults who received one of two types of diets assigned
randomly for a period of 6 weeks. After 6 weeks, the subjects were switched
back to the other diet. The first diet provided 17% of energy as fructose
and the other diet was sweetened with glucose and did not contain any fructose.
Both diets contained common foods and nearly identical amounts of the macronutrients.
The results showed that in men, the fructose diet raised plasma triglyceride
levels by 32% from baseline, although interestingly there was no effect
seen with the women being studied.
While the "normal" upper limits of blood triglyceride level can be as
high as 160 mg/dl, the appropriate goal for optimum
health should not
be higher than 100 mg/dl, with a total triglyceride to HDL cholesterol
level of no higher than 3 (preferably under 2).
Studies have shown that a triglyceride count
of 100 mg/dl above normal levels increases the relative risk of a new cardiovascular
event by 50% and reduces the chance of surviving a subsequent heart attack.
High levels of triglyceride are related to a dietary intake of simple carbohydrate
such as cakes and white bread and starchy food such as pasta, rice and potatoes.
It can be elevated in a diet high in saturated fats, but the correlation
is less dramatic when compared to that of a carbohydrate diet. As such, we can solve this high triglyceride level problem by changing our diet.
We should be able to see a steady decline in the triglyceride level within
a few weeks if a proper low glycemic anti-aging diet is followed.
The role of triglyceride has been under-appreciated for the past 30 years.
Today, nutritional scientists realize that triglyceride is in fact the key
link that connects carbohydrates to obesity, and not dietary fats or dietary
cholesterol. As such, the dominant factor of high triglyceride is carbohydrates
and not fats. In other words, a high triglyceride
level is almost synonymous to a high carbohydrate diet and not a high fatty
diet.
Bad Carbohydrates
Let us now look at how simple and refined carbohydrates such as white bread
and white flour, or starchy carbohydrate foods such as potatoes and rice,
can increase your risk of heart disease. Both are considered "bad".
1. The higher the intake of such carbohydrates, the higher the blood sugar
level in our bodies. This in turn triggers the release of more insulin from
the pancreas in an attempt to normalize the blood sugar. The increased insulin
triggers the liver to produce more VLDL, a triglyceride carrier. The
more VLDL produced, the more triglyceride (blood fat) will circulate
in our blood (remember that VLDL is a carrier of triglyceride). The higher
the VLDL, the higher its metabolite, "bad" LDL cholesterol. Therefore,
increased triglyceride levels and LDL are both proven independent risk factors
for heart disease. It should be noted that scientists are now uncovering
that LDL in and of itself is not "bad". LDL is simply
a carrier of cholesterol in the blood. The problem is that when LDL is bounded
to cholesterol, the resultant LDL-cholesterol
is easily oxidized or made rancid, and this sets up the condition
for inflammatory response at the endothelium, leading to arterial plaques.
LDL becomes oxidized because of bad dietary habits such as a high intake
of refined carbohydrates, stressful lifestyles, and a lack of antioxidants. The solution to reduce LDL-cholesterol is
simple - reduce refined carbohydrate intake, reduce stress, and increase
the intake of antioxidants such as vitamin C, A, and E.
2. Cholesterol can be transferred between the "good" HDL cholesterol and
"bad" LDL cholesterol by an enzyme called cholesteryl ester transfer protein
(CETP), exchanging the "good" HDL cholesterol for triglyceride. With more
triglyceride-rich VLDL, more cholesterol CETP will transfer from your
HDL to your VLDL, thus lowering the HDL level. With less HDL and more
VLDL, the risk of heart disease will go up.
3. In addition to the high level of VLDL and chylomicrons in the blood after
a meal high in simple carbohydrate and starchy food, the chylomicron
remnants and VLDL remnants also increases. A good illustration will
be like a highway during rush hour, when the exit lanes are jammed and all
cars exit more slowly. Similarly, a meal heavy in starchy food, simple carbohydrates
and saturated fats causes post-prandial lipemia ("fatty" blood after a meal).
Chylomicron remnants and VLDL remnants are "jammed" in the blood stream
longer than usual, increasing the risk of heart disease.
|
Continue Reading...
Previous |
1 | 2 | 3 | 4 | 5 | 6 | Next
|
 |
 |
|
|
|
|
|
